Pollutionis the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to theecosystemi.e. physical systems or living organisms.Pollution can take the form ofchemical substanceorenergy, such as noise, heat, or light. Pollutants, the elements of pollution, can be foreign substances or energies, or naturally occurring; when naturally occurring, they are considered contaminants when they exceed natural levels. Pollution is often classed aspoint sourceornonpoint source pollution.